Heretofore, a high-power brushless motor has been used in a hybrid electric vehicle and an electric vehicle. For control of such brushless motor mounted in the hybrid electric vehicle, it is necessary to precisely detect a rotation position of an output shaft of a motor. Because a rotation position of a rotor has to be accurately detected in order to control switching of energization to each coil of a stator. For a vehicle, particularly, there is a demand for reducing cogging that is apt to deteriorate drivability. Thus, accurate switching of energization to each coil is highly requested.
For detection of the location of a vehicle motor shaft, a resolver is used because of its performances such as high-temperature resistance, noise resistance, vibration resistance, and high-humidity resistance. The resolver is mounted in the motor and directly attached to the rotor shaft of the motor.
For instance, a resolver of Patent Literature 1 is arranged such that a high frequency wave is amplitude-modulated by a sine wave and a cosine wave. The amplitude-modulated high-frequency wave is input as an excitation signal to an excitation coil. This can provide an effect of reducing the number of windings of the excitation coil. Herein, the sine wave, the cosine wave, and the high-frequency wave are analog waves.
The control unit calculates an angular displacement based on a phase difference between a zero cross point of the excitation signal input to the excitation coil and a zero cross point of a detection signal output from a search coil.